Weed Seed Movement Via Combines

Crop harvest is here and that means it’s time to be thinking about weed seedbank management. Over the last few weeks we have observed fields throughout Wisconsin with a fair amount of weed escapes. The most troublesome weeds in Wisconsin, waterhemp and giant ragweed, will retain their seeds well into October in the Upper Midwest. If you have weeds that have set seed in your field, now is the time to get out there, remove and burn them before combines start rolling. Check the “UW-NPM Weed Seed Management at Crop Harvest (PDF file)” handout used in our Combine Cleaning Workshops.

If you are unable to remove weeds that have gone to seed, it is important to develop a sound harvest strategy to minimize the spread of weeds from field to field. This would include cleaning combines between fields and harvesting fields with severe weed infestations last.

Last fall, to validate our concerns of weed seed movement via combines, we put out a call to UW-Madison Ag Extension Educators and stakeholders to take the time to clean and collect samples from combines before putting them away for the winter. We specifically asked for samples from four locations: head, feeder house, rock trap, and rotor:

In total we received 31 samples from nine different combines (many thanks to all project participants). We then mixed the samples with field soil and potting mix in our greenhouse and observed what weeds emerged after two weeks.

Check out the results by downloading this handout: “Weed Seed Movement Via Combines: 2019-2020 Case Study (PDF file)”

Here are some of the highlights:

  • 97% of samples contained viable weed seed
  • Combine head samples contained ~49% of the total weeds emerged, followed by the feeder house ~30%, rock trap ~19%, and rotor ~2%
  • Most frequently observed weeds were grasses, pigweeds and common lambsquarters
  • When time is limited, we believe that prioritizing the front of the combine (head and feeder house) would provide the most benefit in reducing weed seed spread by combines

Some additional tips for cleaning combines and reducing the spread of weeds:

  • Use an air compressor or leaf blower to force air through and clear debris from critical portions of the combine
  • Run a bag of wood shavings through the combine to clean rotor/auger area


  • Nick Arneson (UW-Madison Weed Science Outreach Specialist)
  • Dan Smith (UW NPM Southwest Wisconsin Regional Specialist)
  • Rodrigo Werle (UW-Madison Extension Cropping Systems Weed Scientist)